1. Field of the Invention
This invention relates to a reliability ensuring system for an internal combustion engine, and more particularly to a reliability ensuring system for an internal combustion engine which maintains the reliability of the engine by controlling the operating state of the engine when the value of an engine parameter representing the operating state of the engine goes into such a range as to adversely affect the reliability of the engine.
2. Description of the Prior Art
In internal combustion engines, particularly in supercharged engines, proper measures must be taken in order to ensure engine reliability when the value of an engine parameter representing the operating state of the engine, e.g., engine speed (rpm), negative pressure in the intake passage, amount of intake air, coolant temperature and maximum combustion pressure, goes into such a range as to adversely affect the reliability of the engine.
In Japanese Unexamined Patent Publication No. 51(1976)-129529, there is disclosed a reliability ensuring system for an internal combustion engine in which fuel feed to the engine is immediately interrupted to lower the engine rpm when the engine rpm exceeds a preset limit value. However, this system is disadvantageous from the following viewpoint. If the preset limit value is determined on the basis of normal operating state of the vehicle, the engine speed could be lowered when the engine speed temporarily exceeds the preset limit value, for instance, during acceleration for passing and there would arise a danger of being collided into from behind, while if the preset limit value is set at a value higher than that determined on the basis of the normal operating state, the reliability of the engine is adversely affected when the engine rpm is long kept at a value slightly lower than the preset limit value. Generally, deviation of the operating state from the normal operating state should be permitted or is needed for proper driving of the vehicle and does not adversely affect the reliability of the engine so long as the degree of the deviation is relatively small and the duration thereof is relatively short, while the deviation could adversely affect the reliability of the engine if it continues for a long time even if its degree is relatively small. Further, a deviation of large degree could adversely affect the reliability of the engine even if its duration is short.